https://scholars.lib.ntu.edu.tw/handle/123456789/297449
Title: | Osmium(II) complexes of 2-[(arylamido)phenylazo]pyridines. New examples of deamination reactions - X-ray structure and redox properties | Authors: | Das, C. Peng, S.-M. Lee, G.-H. Goswami, S. SHIE-MING PENG |
Issue Date: | 2002 | Journal Volume: | 26 | Journal Issue: | 2 | Start page/Pages: | 222-228 | Source: | New Journal of Chemistry | Abstract: | Reaction of [NH4]2[OsBr6] with 2-[(arylamino)phenylazo]pyridine, NH4C5N=NC6H4N(H)C6H 4(R) [R = H (HLa) or CH3 (HLb)], in the presence of dilute NEt3 affords multiple products. Five compounds of molecular formulas [Os(HL)(L)Br], 1, [Os(L)(pap)Br], 2, two isomers of [Os(pap)2Br2], 3 and 5, and [Os(HL)(pap)Br2], 4, where L and pap stand for the conjugate base of HL and 2-(phenylazo)pyridine, respectively, have been separated on a preparative TLC plate. The X-ray structures of the new and representative complexes 1a, 2a and 4a have been solved to characterise them. The complexes 3 and 5 were characterised by comparing their spectral properties with those of the known and analysed samples of isomeric [Os(pap)2Br2]. Except for complex 1, the rest are formed due to cleavage of an otherwise unreactive C(phenyl)-N(amine) bond which is promoted by the metal ion. The bidentate-tridentate combination of HL and L in 1 is due to electronic factors. Structural data of the compounds have revealed very strong metal-ligand interactions. Osmium(II)-ligand interactions with the neutral azo ligands, viz. HL or pap, are stronger than those with the anionic L ligand. All of the complexes display resolved 1H NMR spectra. However, the spectral pattern is complex due to serious overlap of the resonances. There are multiple electronic transitions in the range 1200-220 nm. The lowest energy transition (HOMO → LUMO) is presumably due to metal-to-ligand charge transfer (MLCT). These complexes undergo multiple and successive one-electron redox processes. The lowest potential anodic response, in each case, has been assigned to the OsII/OsIII couple. E1/2 of this response in 1 and 2 is similar and occurs near 0.45 V. Low oxidation potentials of the above couples allowed the generation of [1a]+ and [2a]+ in solution by exhaustive constant potential coulometry. The trivalent osmium complexes showed rhombic EPR spectra at 77 K. Distortion parameters using the observed g values have been computed. |
URI: | http://www.scopus.com/inward/record.url?eid=2-s2.0-0036174018&partnerID=MN8TOARS http://scholars.lib.ntu.edu.tw/handle/123456789/297449 |
DOI: | 10.1039/b108507g | SDG/Keyword: | azo compound; metal ion; osmium derivative; pyridine derivative; article; chemical structure; deamination; ligand binding; oxidation reduction reaction; priority journal; proton nuclear magnetic resonance; structure analysis; synthesis; thin layer chromatography; X ray analysis |
Appears in Collections: | 化學系 |
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